The so-called BMA process (hydrocyanic acid-methane-ammonia process) for the production of hydrogen cyanide or hydrocyanic acid as is known starts from methane and ammonia and operates in the absence of oxygen or air.
The reaction itself is carried out in suspending reaction tubes made of sintered aluminum oxide, which are lined internally with a platinum catalyst.
The connection between these ceramic reaction tubes and the gas distribution suitably takes place via a copper tulip, see, e.g. FIG. 4 and Endter German Pat. No. 959,364 and related Endter et al U.S. Pat. No. 2,987,382. The entire disclosures of the Endter et al U.S. patent and the Endter German patent are hereby incorporated by reference and relied upon.
Since the reaction proceeds endothermically the reaction tubes are heated and thereby reaction temperatures maintained at around 1300.degree. C. In order to avoid the occurrence of the reverse reaction the hydrogen cyanide containing gaseous mixture formed must be cooled quickly to temperatures below 400.degree. to 300.degree. C. which takes place in a water cooled chamber made of aluminum in the furnace top itself, see Ullmann, Enzyklopadie der technischen Chemie, 4th edition, Vol. 9 pages 657-659, particularly 659; Dechema-Monograph, 1959, number 33 pages 28-46 and also German Pat. No. 959,364 and Endter et al U.S. Pat. No. 2,987,382.
According to German application P No. 29 13925.1-41 and related Voigt U.S. application Ser. No. 133,358 filed Mar. 24, 1980 it has also been proposed already to employ liquified aliphatic hydrocarbon gases in place of methane. The entire disclosure of the Voigt U.S. application is hereby incorporated by reference and relied upon.
In employing methane the yield of hydrogen cyanide is about 85 volume % of theory based on the ammonia employed and about 90 volume % of theory based on the methane employed, see Ullman loc. cit.
Before the recovery of free hydrogen cyanide from the product gas stream the unreacted ammonia must be removed in some form from the product gas stream, e.g. with dilute sulfuric acid as ammonium sulfate. This requires an additional expense and besides additional costs.
The object of the process of the invention therefore is to increase the yield of hydrogen cyanide in the hydrocyanic acid-methane-ammonia process and also to reduce the portion of ammonia in the product gas.